Several processes for dealing with considerations of tool path offset currently exist.
(1) N-item Lookahead:
This method is limited to searching forward along the tool path for a change in sense such as an arc that was clockwise before offset and became counterclockwise after offset. It fails to detect keyhole interference or allow for coincident tool path segments.
(2) Projected Bisectors:
This method projects geometric bisectors between adjacent geometry items and searches for intersections of bisectors. After all of the bisectors have coincided, a web is formed, from which a tool path may be generated by breaking up the legs of the web and interconnecting them. This method requires a completely enclosed machinable zone, and can only be used inside of a closed contour (a pocket).
(3) Intersection Tree:
This method offsets the tool path and generates an intersection list which is inspected and sorted based upon the nesting level of the intersections within one another. This process is in common use today as it operates quickly and manages special cases well. However, it is expensive in process time and implementation. It relies heavily on special case processing and is thus slow and cumbersome to use.
These existing processes suffer from many shortcomings, including speed and ease of use, special case restrictions, and end application limitations, as discussed hereinabove.
In accordance with the present invention, a system and method of tool path processing is taught which offsets a tool path from a given geometric sequence, avoiding tool interference and accounting for coincident tool paths. It guides a numerically-controlled machine tool in the manufacturing process.
ZONE is used herein to refer to the process and system incorporating the process.
The ZONE process is a two-dimensional geometric offset process which can be used in numerically-controlled machining or computer aided-manufacturing applications.
The ZONE process is used to generate the locus of the center of a circle (representing a tool) as it rolls along a given geometric path, maintaining tangency as it rolls, and guiding the (numerically controlled machine) tool in the manufacturing process.
The ZONE process avoids tool interference problems that would cause the tool to take off excessive material. These problems traditionally fall into two classes:
(a) Small-move interference: A tool must travel into a concave area that is smaller than the tool dimension. In this case, the tool cannot machine the specified area.
(b) Keyhole interference: A tool path crosses a prior (or future) tool path, taking material off from an area that has already been or will be machined. In this case, the tool retracts and moves past the interference area, then resumes machining.
The ZONE process handles the case of coincident tool path, which arises when a tool passes through a channel that is equal in width to the tool diameter.
The ZONE method does not segregate between open contours (those that start at one location and end at another) and closed contours (those that start and end at the same location).